InGaAs/InP double heterostructures on InP/Si templates fabricated by wafer bonding and hydrogen-induced exfoliation

Hydrogen-induced exfoliation combined with wafer bonding has been used to transfer ~600-nm-thick films of (100) InP to Si substrates. Cross-section transmission electron microscopy (TEM) shows a transferred crystalline InP layer with no observable defects in the region near the bonded interface and an intimately bonded interface. InP and Si are covalently bonded as inferred by the fact that InP/Si pairs survived both TEM preparation and thermal cycles up to 620 °C necessary for metalorganic chemical vapor deposition growth. The InP transferred layers were used as epitaxial templates for the growth of InP/In0.53Ga0.47As/InP double heterostructures. Photoluminescence measurements of the In0.53Ga0.47As layer show that it is optically active and under tensile strain, due to differences in the thermal expansion between InP and Si. These are promising results in terms of a future integration of Si electronics with optical devices based on InP-lattice-matched materials

Therapy-based exercise from the perspective of adult patients: a qualitative systematic review conducted using an ethnographic approach

© The Author(s) 2019.Objectives: Many patients do not meet recommended levels of therapy-based exercise. This review aims to explore how adult patients view being prescribed therapy-based exercise, the information/education they are given and receive and if/how they independently practise and adhere. Design: A qualitative systematic review conducted using an ethnographic approach and in accordance with the PRISMA statement. Sources: PubMed, CINAHL, SCOPUS and EMBASE databases (01 January 2000–31 December 2018). Methods: Qualitative studies with a focus on engagement/adherence with therapy-based exercise were included. Data extraction and quality appraisal were undertaken by two reviewers. Results were discussed and data synthesized. Results: A total of 20,294 titles were screened, with data extracted from 39 full texts and data from 18 papers used to construct three themes. ‘The Guidance received’ suggests that the type of delivery desired to support and sustain engagement was context-dependent and individually situated. ‘The Therapist as teacher’ advocates that patients see independent therapy-based exercise as a shared activity and value caring, kind and professional qualities in their therapist. ‘The Person as learner’ proposes that when having to engage with and practise therapy-based exercise because of ill-health, patients often see themselves as new learners who experience fear and uncertainty about what to do. Patients may have unacknowledged ambivalences about learning that impact on engagement and persistence. Conclusion: The quality of the interaction between therapists and patients appears integral to patients engaging with, and sustaining practice of, rehabilitation programmes. Programmes need to be individualized, and health care professionals need to take patients’ previous experiences and ambivalences in motivation and empowerment into account.Peer reviewe

Imaging charge and spin diffusion of minority carriers in GaAs

Room temperature electronic diffusion is studied in 3 mum thick epitaxial p+ GaAs lift-off films using a novel circularly polarized photoluminescence microscope. The method is equivalent to using a standard optical microscope and provides a contactless means to measure charge (L) and spin (L_s) diffusion lengths. The measured values of L and L_s are in excellent agreement with the spatially averaged polarization and a sharp reduction in these two quantities (L from 21.3 mum to 1.2 mum and L_s from 1.3 mum to 0.8 mum) is measured with increasing surface recombination. Outwards diffusion results in a factor of 10 increase in the polarization at the excitation spot.Comment: 13 pages, 3 figure

Investigation of Deep Impurity Levels in CdTe/CdS Solar Cells

We have studied deep impurity levels of CdTe/CdS solar cells by capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS) and time-resolved photoluminescence (TRPL)

InGaAs/InP double heterostructures on InP/Si templates fabricated by wafer bonding and hydrogen-induced exfoliation

Hydrogen-induced exfoliation combined with wafer bonding has been used to transfer similar to600-nm-thick films of (100) InP to Si substrates. Cross-section transmission electron microscopy (TEM) shows a transferred crystalline InP layer with no observable defects in the region near the bonded interface and an intimately bonded interface. InP and Si are covalently bonded as inferred by the fact that InP/Si pairs survived both TEM preparation and thermal cycles up to 620 degreesC necessary for metalorganic chemical vapor deposition growth. The InP transferred layers were used as epitaxial templates for the growth of InP/In0.53Ga0.47As/InP double heterostructures. Photoluminescence measurements of the In0.53Ga0.47As layer show that it is optically active and under tensile strain, due to differences in the thermal expansion between InP and Si. These are promising results in terms of a future integration of Si electronics with optical devices based on InP-lattice-matched materials

Stress-driven instability in growing multilayer films

We investigate the stress-driven morphological instability of epitaxially growing multilayer films, which are coherent and dislocation-free. We construct a direct elastic analysis, from which we determine the elastic state of the system recursively in terms of that of the old states of the buried layers. In turn, we use the result for the elastic state to derive the morphological evolution equation of surface profile to first order of perturbations, with the solution explicitly expressed by the growth conditions and material parameters of all the deposited layers. We apply these results to two kinds of multilayer structures. One is the alternating tensile/compressive multilayer structure, for which we determine the effective stability properties, including the effect of varying surface mobility in different layers, its interplay with the global misfit of the multilayer film, and the influence of asymmetric structure of compressive and tensile layers on the system stability. The nature of the asymmetry properties found in stability diagrams is in agreement with experimental observations. The other multilayer structure that we study is one composed of stacked strained/spacer layers. We also calculate the kinetic critical thickness for the onset of morphological instability and obtain its reduction and saturation as number of deposited layers increases, which is consistent with recent experimental results. Compared to the single-layer film growth, the behavior of kinetic critical thickness shows deviations for upper strained layers.Comment: 27 pages, 11 figures; Phys. Rev. B, in pres

Electrocatalityc application of gold-polyaniline nanocomposite

Gold‒polyaniline (AuPANI) nanocomposite, with granular morphology of PANI and rod‒like Au nanoparticles (NPs) as dominate structure distributed in it, was prepared by interfacial polymerization method in an immiscible water/toluene biphasic system. Simultaneously with the aniline polymerization to polyaniline (PANI) by HAuCl4, as an oxidant, AuNPs are formed. AuPANI composite as green precipitate is collected from aqueous phase. Polyaniline in the composite is in the conductive emeraldine salt form (PANIES), with high amount of Au (28.85 wt %). Nanocomposite showed great electrocatalytic activity towards the electrochemical O2reduction reaction (ORR), with high ORR onset potential and high selectivity for O2reduction to water. This makes it a good candidate for a new class of Pt‒free ORR catalyst.Physical chemistry 2016 : 13th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-30 September 2016

The Spectral Energy Distribution of HH30 IRS: Constraining The Circumstellar Dust Size Distribution

We present spectral energy distribution (SED) models for the edge-on classical T Tauri star HH30 IRS that indicate dust grains have grown to larger than 50 microns within its circumstellar disk. The disk geometry and inclination are known from previous modeling of multiwavelength Hubble Space Telescope images and we use the SED to constrain the dust size distribution. Model spectra are shown for different circumstellar dust models: a standard ISM mixture and larger grain models. As compared to ISM grains, the larger dust grain models have a shallower wavelength dependent opacity. Models with the larger dust grains provide a good match to the currently available data, but mid and far-IR observations are required to more tightly constrain the dust size distribution. The accretion luminosity in our models is L_acc<0.2 L_star corresponding to an accretion rate of 4E-9M_sun/yr. Dust size distributions that are simple power-law extensions (i.e., no exponential cutoff) yield acceptable fits to the optical/near-IR but too much emission at mm wavelengths and require larger disk masses. Such a simple size distribution would not be expected in an environment such as the disk of HH30 IRS, particularly over such a large range in grain sizes. However, its ability to adequately characterize the grain populations may be determined from more complete observational sampling of the SED in the mid to far-IR.Comment: ApJ Accepte

Spin-dependent transport in metal/semiconductor tunnel junctions

This paper describes a model as well as experiments on spin-polarized tunnelling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate spin-polarized carriers. A transport model is presented that takes account of carrier capture in the semiconductor surface states, and describes the semiconductor surface in terms of a spin-dependent energy distribution function. The so-called surface spin-splitting can be calculated from the balance of the polarized electron and hole flow in the semiconductor subsurface region, the polarized tunnelling current across the tunnel barrier between the magnetic material and the semiconductor surface, and the spin relaxation at the semiconductor surface. Measurements are presented of the circular-polarization-dependent photocurrent (the so-called helicity asymmetry) in thin-film tunnel junctions of Co/Al2O3/GaAs. In the absence of a tunnel barrier, the helicity asymmetry is caused by magneto-optical effects (magnetic circular dichroism). In the case where a tunnel barrier is present, the data cannot be explained by magneto-optical effects alone; the deviations provide evidence that spin-polarized tunnelling due to optical spin orientation occurs. In Co/τ-MnAl/AlAs/GaAs junctions no deviations from the magneto-optical effects are observed, most probably due to the weak spin polarization of τ-MnAl along the tunnelling direction; the latter is corroborated by bandstructure calculations. Finally, the application of photoexcited GaAs for spin-polarized tunnelling in a scanning tunnelling microscope is discussed.